Study On The Support Mechanism And Stability Control Of The TBM Tunnelling In Deep Mixed Strata

TBM tunnelling has been widely used in the construction of transportation,water conservancy and mines.Tunnels constructed in mountain regions often face challenges of high in-situ stress in deep ground and mixed strata with soft rock formation,which constitute the basic condition of squeezing large deformation and might lead to tunnel destruction.Complex geological conditions are often encountered in TBM engineering in deep mixed strata.Understanding the mechanism of the supporting system has a significant impact on the stability control of the surrounding rock.This thesis was supported by the National 973 project.Laboratory experiment,numerical simulation,theoretical analysis and intelligent algorithm were applied in this study,as well as a computer vision monitoring system for geotechnical deformation with a feature.The mechanical properties and failure features of the mixed strata specimens,the deformation of the surrounding rock and supporting effects of TBM tunnelling in deep mixed strata as well as the stability control by non-uniform supports were studied in details.The main results are as follows:(1)The mixed strata specimens were prepared by mudstone and sandstone with structural planes in certain cohesion.Confined compression tests were conducted on the specimens using a rock mechanics servo-controlled testing system.The mechanical properties and failure characteristics of the specimens were analyzed.The strength anisotropy is greater than the deformation anisotropy.Acoustic emission(AE)properties are significantly affected by the inclination angle and incompatible deformation.(2)A medium and small tunnel physical simulation test system based on biaxial motor loading was developed.The testing system comprised a loading test system,model boxes and support simulation devices.The test system is powered by active servo motors,which can provide complex in-situ stress state of the deep tunnel engineering.The model boxes of the tunnel cross and longitudinal sections and the multiple support were developed to equip this test system,which makes the model tests possible.(3)The deformation and failure characteristics of the surrounding rock for TBM tunnelling in deep mixed strata were analyzed under different conditions.Incompatible deformation between the soft rock and hard rock in mixed strata controls the failure process.An experimental method based on artificial neural network was proposed to predict the whole deformation process and failure mode of mixed strata,which provides a new method to study the support mechanism of the TBM tunnelling in deep mixed strata.(4)By model test and numerical simulation,the support mechanism of the TBM tunnelling in deep mixed strata was revealed.Supporting efforts reduce the deformation of the surrounding rock,increase the uniformity and mobilize larger scale surrounding rock to bear the loads.Moreover,supporting efforts improve the integrity and compatible deformation between the soft rock and hard rock in mixed strata,mobilize the bearing capacity of surrounding rock and reduce the damage zone at soft rock and structure plane,as well as the supporting function of hard rock on soft rock.(5)To control the incompatible deformation of the deep mixed strata,a new “lining+non-uniform shear resistant bolt” combined support is proposed to maintain the stability of the surrounding rock.Incompatible deformation of the mixed strata can be effectively controlled by this support design,which could improve the local stress state of the lining.The new combined support method provides references for the design of the TBM tunnelling in deep mixed strata.The results are of some theoretical and practical value in understanding the support mechanism and the stability control of the TBM tunnelling in deep mixed strata.There are 89 figures,17 tables and 145 references in this dissertation.